6. Refractive Errors and Paeds Flashcards
How does one assess visual acuity in Adults?
Snellen Chart
Describe the Snellen Chart procedure and how the result is arrived at?
Patient sits at 6 meters from chart
Vision expressed as a fraction – eg 6/36 – means that at 6m from the chart, patient can read what someone with “normal” vision would be expected to read from further back at 36m
What should be checked if the patient cannot read the top line of a Snellen Chart?
CF – count fingers?
HM – hand movements?
PL – perception of light?
NPL – no perception of light?
Term used to describe ‘no refractive errors’
Emmetropia
Term used to describe ‘shortsighted’
Myopia
Term used to describe ‘longsighted’
Hyperopia
Term used to describe when two eyes have unequal refractive power.
Anisometropia
Loss of accommodative power with increasing age.
Presbyopia
Decreased vision that results from abnormal visual development in infancy/childhood
Amblyopia
Blurred vision due to irregular shape of cornea – making it difficult to get light in focus on the retina
Astigmatism
What is myopia?
Optical power of the eye is too strong for it’s corresponding axial length, thereforethe light is focused in front of the retina – so a blurry image falls on the retina.
Often due to longer than normal eye.
How is myopia corrected?
Concave Lens (Minus)
What are the categories of myopia and their characteristic?
NON-PATHOLOGICAL MYOPIA
Usually less than 6.0 dioptres
Onset in childhood/adolescence
Usually progresses through adolescent growth phase, and stabilises in second decade
PATHOLOGICAL MYOPIA
Usually greater than 6.0 dioptres
Usually presents in early childhood and is progressive
Risk of vision threatening consequences – retinal detachment, choroidal neovascularisation
Discuss the different aetiological factors that contribute to myopia?
GENETIC FACTORS
Family history
High myopia linked to several multi-system diseases – eg Marfan’s, Ehler’s Danlos syndromes
Higher incidence in asian population (80% in asia versus 20-50% in america)
ENVIRONMENTAL FACTORS
Spending more time outdoors in childhood appears to be protective
Higher incidence in people who spend more time doing near work (reading, computers etc)
What are the pathological features/complications of myopia?
Tilted disc
Atrophy of chorioretinal capillaries and RPE
Risk of retinal degeneration and detachment
Risk of choroidal neovscularisation
Associated with POAG
What is the Tx for Myopia?
Glasses – minus (concave lenses)
Contact lenses
Refractive surgery
What is hyperopia?
Weaker refractive power of the eye relative to the axial length
Shorter eye
What is the prevalence of hyperopia
(10%)
What is the prevalence of hyperopia in neonates?
Most babies are hyperopic at birth – this is normal